This invention relates to the preparation of m-aminobenzenephosphonic acid, more particularly involving the use of benzenephosphonous acid through a reaction sequence that includes the nitration of benzenephosphonous acid to form m-nitrobenzenephosphonous acid and subsequent oxidation and reduction to produce the desired m-aminobenzenephosphonic acid.
Various procedures are described in the literature for the preparation of m-aminobenzenephosphonic acid, particularly the extensive work of Michaelis in the later 1800's as reported in Beilstein 16:791. A review of this and other literature does not disclose the nitration of benzenephosphonous acid and its subsequent oxidation.
The commercial preparation of m-aminobenzenephosphonic acid commences from benzenephosphonic acid; the present invention uses benzenephosphonous acid which sells for about half of the price of benzenephosphonic acid thus lending commercial advantage to the process disclosed.
The process of the present invention is well suited to commercial operations particularly in its degree of controlability-- that is the absence of explosive conditions attained during the process. For instance, in the preparation of m-aminobenzenephosphonic acid from benzenephosphonic acid (sometimes referred to in the literature as phenylphosphonic acid) various procedures instruct the operator to use extreme care in the nitration portion of the process as the nitration reaction itself is extremely exothermic. Even with the use of low temperatures eruptions or explosions may occur using the phosphonic acid starting material.
The m-aminobenzenephosphonic acid is useful as an intermediate in the synthesis of organophosphorus-type dyes and its use is described in more detail in Swiss Application No. 7273/73 filed May 22, 1973 laid open to public inspection on Sept. 15, 1975, and German Offenlegungsschrift P 23 24 809.1 filed May 16, 1973, open to public inspection on Dec. 20, 1973, the disclosures of which are hereby incorporated by reference.